Low temperature clayden prescreening



Nov. 12, 1963 J. A. c. YULE 3,110,593

LOW TEMPERATURE CLAYDEN PRESCREENING I Filed Nov. 14. 1960 l E2191 I I 1l7 (f [fl/Il/I/l/I/l/l/I/l/l/ l/l/l/l/j/l/l; IcE.\ P12 /////////////y//L V3 JbhmAU. Yu l e IN VEN TOR.

BY WM M MTORNEYS United States Patent 3,110,593 I LGW TEMPERATURECLAYDEN PRESCREENENG John A. C. Yule, Rochester, N.Y., assignor toEastman Kodak Company, Rochester, N.Y., a corporation of New JerseyFiled Nov. 14, 196i), Ser. No. 69,152 6 Claims. (Cl. 96-45) Thisinvention relates to the prescreening of film for use in halftonereproduction work. A prescreened film'is one which has variations insensitivity distributed in halftone pattern.

Clayden prescreening of film is described in US. Patent 2,691,586, to J.A. C. Yule and R. E. Maurer. Cross reference is made to two cofiledapplications, Serial No. 69,153 by Donald J. Howe, entitled PrescreeningFilm by Clayden and Herschel Exposure, and Serial No. 69,154 by DonaldJ. Howe and Richard E. Maurer, entitled Continuous Prescreening of Film.

The present invention is based on a discovery of a relationship betweenthe temperature of the silver halide emulsion layers and the Claydeneffect.

I have found that when the temperature of film is lowered to C. orlower, for example by the presence of Dry Ice or liquid air, two thingshappen to the Clayden sensitivity. Clayden sensitivity refers to theamount of desensitization produced 'by a short duration pre-exposure,and is measured in terms of the relative log exposure (low intensity,long duration) required to produce a latent image with and without thedesensitization preexposure. Even films which show a very low Claydensensitivity exhibit a much higher sensitivity at these lowertemperatures. However, the present invention is concerned primarily withthose materials which already show a fairly high Clayden sensitivity atroom temperature, say 20 C. specifically which show at least 0.3 log Eunits Clayden effect to a high intensity exposure of 0.001 second at 20C. All such materials when cooled to below 10 C. show a greatly enhancedClayden effect, some materials have actually shown over 1.6 log E unitsClayden chest at -40 v C., but this is beyond that required by ordinaryprescreening procedures although it may be useful for special pur- Thesecond effect, and this is perhaps the more poses.

important one, is that the low temperature extends the exposure timewhich is permissible without losing the Clayden effect.

Thus one object of the invention is to provide greater scale thanpreviously obtainable by Clayden prescreening and another object is toprovide a manner of continuously Clayden prescreening.

Historically Clayden effects require brief exposures, usually less thana 50th of a second. At temperatures below 10 C. the Clayden effect isstill observed in a useful amount up to one second exposure time andeven up to a few seconds, say four. Because of this longer duration, theuse of the term Clayden effect under these circumstances might, at firstsight, be questioned, but it is proper and applicable since the effectis the same, although the difference was not predicted. While the upperlimit of exposure duration at room temperature is on the order ofsecond, this upper limit increases by a factor of two for about every 10C. drop in temperature. Dropping the temperature from +20 C. to 10 C.increases the time limit about 8 times. However, temperatures of 40 C.or lower are preferred; the drop from +20 C. to 40 C. increases the timelimit about 64 times. This means that exposure in excess of /2 secondcan be used and this in turn lends itself admirably to continuousClayden prescreening of film. Thus a preferred embodiment of theinvention moves a chilled photosensitive layer through an exposurestation synchronously with a halftone exposing image while giving anexposure of sufficiently high intensity and sufficiently short duration(in this case less than 4 seconds) to produce Clayden desensitization ina useful amount, say at least 0.6 log E units. So that the exposurestation will not be impractically narrow in the direction of movement ofthe film and so that the film will not have to move impractically fast,an exposure lasting at least /2 second is preferable. Thus one preferredembodiment of the invention has an exposure between /2 second and 4seconds, the film being sufficiently chilled to give Clayden effect forexposures of such duration. The moving exposing image is provided eitherby a moving screen (ruled or contact type) with a fixed light source orby a fixed ruled screen and a moving source or exposing aperture.

There appears to be nothing peculiar in the emulsion I selected for thispurpose. Any photosensitive silver halide emulsion which shows at least0.3 log E units of desensitization when given an exposure of 0.001second (and of proper intensity) at a temperature of 20 C., will givethe added effects necessary for the operation of the present invention.As is known, total exposure (intensity times time) is just belowthreshold for maximum Clayden effect. The briefness of the durationrequires the intensity to be high even though threshold is barelyreached.

The operation of the invention will be more fully understood when readin connection with the accompanying drawing in which:

FIG. 1 schematically illustrates one embodiment of the invention and,

FIG. Zschematically illustrates continuous prescreening according to theinvention.

In FIG. 1 a silver halide emulsion layer 10 which at 20 C. will show 0.3log E units Clayden effect to brief exposure, is carried on a support 11which in turn rests on a metal container 12 containing Dry Ice 13 tobring the emulsion layer 10 to the temperature of Dry Ice which is about56 C. The operation must be performed in a dry atmosphere to preventcondensation of moisture on the emulsion layer 1 Light from a lamp 16 asindicated by arrows 17 exposes the layer 10 through a ruled halftonescreen illustrated schematically at 18. The exposure at the emulsionlayer it at halftone distance behind the ruled screen 18 is in anundulating pattern due to the size of the source 16 and diffractioneffects at the apertures in the screen 18. This is a normal halftoneexposure step. If the lamp 16 is a flash lamp giving exposures of fl ofa second say, the Clayden desensitization in the areas-of the layer 10which are exposed, will be very high, about 1.2 to 1.6 or 1.8 log Eunits. This is an excellent way to get a high degree of Claydenprescreening. If the lamp to is an ordinary tungsten lamp for examplethe exposure may be permitted to continue for about 1 secondand the film1% still receives a useful degree of Clayden prescreen- In FIG. 2, theability to getClayden prescreening with relatively long duration ofexposure is put to use to provide continuous prescreening. A film 20,emulsion side down, is rolled from a supply roll 21 and is passedthrough a cooling chamber 22. Chilling rollers come in contact with theemulsion or the back of the film or, as shown, with both sides of thefilm. These chilling rollers are kept very cold by the circulation of alow temperature liquid (say liquid air) from a supply 26 by means or" apump 27. Alternatively the rollers may be chilled by direct contact withDry Ice. Again the film is preferably kept in a dry atmosphere duringand following chilling to the low temperature. transparent roller 30carrying a contact halftone screen 31 on the surface thereof. Lig itfrom a lamp 32 exposes the film while it passes from the point 33 to thepoint 34. A mask or reflector 35 confines the light to this area of Thefilm is then passed over a the drum. The exposure station between points33 and provides about /2 second exposure as the film moves to a talteuproll This contact halftone screen 31 on a transparent roller is similarto those used in the continuous preparation of contact halftone screenmaterial. Projection printing is less preferable because of the addeddir'liculty in obtaining suhiciently high intensity. The drum or roller33 moves relative to the mask 35. The driving mechanism (which mayengage the ends of the drum) is not shown. Preferably the edges of thefilm are held by pressure rollers to an easily rotated drum and the filmitself then drives the drum to insure that tl ere is no slippage betweenthe film and the drum. The main drive for the film is provided on thetakeup roll by any suitable drive means, not shown. it is preferable touse a contact halftone screen in this continuous prescrcening form ofthe invention, but a sharp screen spaced from the film by a glass drum(or in a fiat exposure station by air) may be used. in the case of aflat station, the film may be ctually spaced from the halftone screenwith the film support in contact with rollers or t er means formaintaining the spacing of the film from therscreen. The Herschelclean-up features described in the copending applications referred toabove may be combined with this low temperature Clayden prescreening toprovide the advantages of both.

Various systems in which a halftone screen is held stationary and a filmis moved continuously relative thereto are described in US. latent2,211,345, Murray. in these systems an exposing image (behind thescreen) moves synchronously with the film by the simple expedient ofmoving the exposing light aperture. Such arrangements are directlyuseful with the present invention which lengthens the permissible timeof the Clayden exposure so that the film can move completely across theexposing station during the brief (eg. one second) exposure at whichClayden effect (at -40 C.) occurs. Thus, cooling Clayden sensitive filmto C., preferably to 40 (3., and exposing it as shown in US. 2,211,345,produces a prescreened (desensitized) film according to the presentinvention instead of producing the contact screen of Murray.

Having thus described preferred embodiments of my invention I point outthat it is not limited thereto but is of the scope of the appendedclaims.

I claim:

1. The method of making a halftone sensitive material which comprisescooling to a temperature below l0 C. a photosensitive silver halideemulsion layer of the type which at C. temperature shows at least 0.3log E units (Hayden ellect to high intensity exposures of 0.001 second,erqzosins said layer at said low temperature through a halftone screento a high intensity, short duration, uniform exposure of suiiicientintensity and sufiiciently short duration to produce a Claydendesensitization of at least 0.6 log E units, the illumination at theemulsion being dist 'buted in an undulating halftone pattern.

2. The method according to claim 1 in which said exposin includescontinuously moving the layer and exposli ht pattern past an exposurearea, the duration bein g between /2. second and 4 seconds.

3. The method of continuously prescreening a photosensitive silverhalide emulsion layer of the type which at 20 C. temperature shows atleast 0.3 log E units Clayden effect to high intensity exposures of0.001 second, which comprises cooling the layer to a temperature belowl0 C., moving the layer while so cooled through an exposurestationsynchron usly with a light image having an undulating halitonepattern caused by an adjacent halftone screen and exposing the layer bysaid image through the screen to a high intensity, short duration,uniform exposure of sufficient intensity and sufiiciently short durationto produce a Clayden desensitization of at least 0.6 log E units.

4. The method according to claim 3 in which the layer is in contact witha contact halftone screen and the two move together through the exposurestation.

5. The n ethod according to claim 3 in which the halftone screen is astationary ruled screen at halftone spacing in front of the exposurestation and an illuminated area moves transversely in front of thescreen so that the halftone image formed by li ht from the illuminatedarea in the exposure area moves synchronously with the layer.

6. The method according to claim 3 in which said cooling is to atemperature below 40 C. and the exposure is between /2 second and 4seconds.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES James et al.: Fundamentals of Photographic Theory, 2d

ed., Morgan and Morgan 1110., New York, pages -57, 7374 and 77-79.

1. THE METHOD OF MAKING A HALFTONE SENSITIVE MATERIAL WHICH COMPRISESCOOLING TO A TEMPERATURE BELOW -10*C. A PHOTOSENSITIVE SILVER HALIDEEMULSION LAYER OF THE TYPE WHICH AT 20*C. TGEMPERATURE SHOWS AT LEAST0.3 LOG E UNITS CLAYDEN EFFECT TOGHITH INTENSITY EXPOSURES OF 0.001SECOND, EXPOSING SAID LAYER AT SAID LOWER TEMPERATURE THROUGH A HALFTONESCREEN TO A HIGH TENSITY, SHORT DURATION, UNIFORM EXPOSURE OF SUFFICIENTINTENSITY AND SUFFICIENTLY SHORT DURATION TO PRODUCE A CLAYDENDESENSITIZATION OF AT LEAST 0.6 LOG E UNITS, THE ILLUMINATION AT THEEMULSION BEING DISTRIBUTED IN AN UNDULATING HALFTONE PATTER.